Uncovering Multiple Metal-Metal Bonding in a Tetranuclear Fluoride Rhenium Cluster or the Curious Case of {[Ni(H2O)(6)](NH4)(4)}[Re4F18]center dot 4H(2)O

摘要

The compound {[Ni(H2O)(6)](NH4)(4)}[Re4F18]center dot 4H(2)O (1) has been isolated and characterized by single-crystal X-ray diffraction, Raman spectroscopy and computational methods. The compound 1 crystallizes in the triclinic space group P1 (a = 6.6620(9) angstrom, b = 9.7121(13) angstrom, c = 11.2007(15) angstrom, alpha = 67.644(2)degrees, beta = 83.827(2)degrees, gamma = 84.366(2)degrees). In 1, the [Re4F18](6-) anion is composed of four Re(III) atoms bridged by two mu-bridging fluorine atoms and two di-mu-bridging fluorine atoms. In [Re4F18](6-), the shortest Re-Re distance (i.e., 2.3631(6) angstrom) is characteristic of the presence of a Re=Re double bond; the Re-F distances range from 1.854(6) to 2.008(5) angstrom. Theoretical calculations confirm the presence of a weak Re=Re double bond; the Mayer-Mulliken bond order of the doubly bridged Re atoms is 1.8097 and the natural localized molecular orbital bond order is 1.8751. The Raman spectrum of 1 has been measured and shows a series of bands in the region 167-1449 cm(-1) that have been attributed to Re-F and Ni-O stretches, Re4F18 ring breathing and NH4+ bending and libration modes.